Organic electroluminescent materials and devices

ABSTRACT

A compound including a Ligand L of Formula I: 
     
       
         
         
             
             
         
       
     
     as well as, a first device and a formulation containing the same, are disclosed. In the compound including the Ligand L of Formula I:
         X is selected from the group consisting of S, Se, SiRR′ and GeRR′;   R 1 , R 2 , R, and R′ are each independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof;   any adjacent substitutions or substituents of R 1 , R 2 , R, and R′ are optionally linked together to form a ring;   the Ligand L is coordinated to a metal M having an atomic number of 40 or greater, and   the Ligand L is optionally linked with other ligands to comprise a tridentate, tetradentate, pentadentate or hexadentate ligand.

PARTIES TO A JOINT RESEARCH AGREEMENT

The claimed invention was made by, on behalf of, and/or in connectionwith one or more of the following parties to a joint universitycorporation research agreement: Regents of the University of Michigan,Princeton University, University of Southern California, and theUniversal Display Corporation. The agreement was in effect on and beforethe date the claimed invention was made, and the claimed invention wasmade as a result of activities undertaken within the scope of theagreement.

FIELD OF THE INVENTION

The present invention relates to compounds for use as emitters anddevices, such as organic light emitting diodes, including the same.

BACKGROUND

Opto-electronic devices that make use of organic materials are becomingincreasingly desirable for a number of reasons. Many of the materialsused to make such devices are relatively inexpensive, so organicopto-electronic devices have the potential for cost advantages overinorganic devices. In addition, the inherent properties of organicmaterials, such as their flexibility, may make them well suited forparticular applications such as fabrication on a flexible substrate.Examples of organic opto-electronic devices include organic lightemitting devices (OLEDs), organic phototransistors, organic photovoltaiccells, and organic photodetectors. For OLEDs, the organic materials mayhave performance advantages over conventional materials. For example,the wavelength at which an organic emissive layer emits light maygenerally be readily tuned with appropriate dopants.

OLEDs make use of thin organic films that emit light when voltage isapplied across the device. OLEDs are becoming an increasinglyinteresting technology for use in applications such as flat paneldisplays, illumination, and backlighting. Several OLED materials andconfigurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and5,707,745, which are incorporated herein by reference in their entirety.

One application for phosphorescent emissive molecules is a full colordisplay. Industry standards for such a display call for pixels adaptedto emit particular colors, referred to as “saturated” colors. Inparticular, these standards call for saturated red, green, and bluepixels. Color may be measured using CIE coordinates, which are wellknown to the art.

One example of a green emissive molecule is tris(2-phenylpyridine)iridium, denoted Ir(ppy)₃, which has the following structure:

In this, and later figures herein, we depict the dative bond fromnitrogen to metal (here, Ir) as a straight line.

As used herein, the term “organic” includes polymeric materials as wellas small molecule organic materials that may be used to fabricateorganic opto-electronic devices. “Small molecule” refers to any organicmaterial that is not a polymer, and “small molecules” may actually bequite large. Small molecules may include repeat units in somecircumstances. For example, using a long chain alkyl group as asubstituent does not remove a molecule from the “small molecule” class.Small molecules may also be incorporated into polymers, for example as apendent group on a polymer backbone or as a part of the backbone. Smallmolecules may also serve as the core moiety of a dendrimer, whichconsists of a series of chemical shells built on the core moiety. Thecore moiety of a dendrimer may be a fluorescent or phosphorescent smallmolecule emitter. A dendrimer may be a “small molecule,” and it isbelieved that all dendrimers currently used in the field of OLEDs aresmall molecules.

As used herein, “top” means furthest away from the substrate, while“bottom” means closest to the substrate. Where a first layer isdescribed as “disposed over” a second layer, the first layer is disposedfurther away from substrate. There may be other layers between the firstand second layer, unless it is specified that the first layer is “incontact with” the second layer. For example, a cathode may be describedas “disposed over” an anode, even though there are various organiclayers in between.

As used herein, “solution processible” means capable of being dissolved,dispersed, or transported in and/or deposited from a liquid medium,either in solution or suspension form.

A ligand may be referred to as “photoactive” when it is believed thatthe ligand directly contributes to the photoactive properties of anemissive material. A ligand may be referred to as “ancillary” when it isbelieved that the ligand does not contribute to the photoactiveproperties of an emissive material, although an ancillary ligand mayalter the properties of a photoactive ligand.

As used herein, and as would be generally understood by one skilled inthe art, a first “Highest Occupied Molecular Orbital” (HOMO) or “LowestUnoccupied Molecular Orbital” (LUMO) energy level is “greater than” or“higher than” a second HOMO or LUMO energy level if the first energylevel is closer to the vacuum energy level. Since ionization potentials(IP) are measured as a negative energy relative to a vacuum level, ahigher HOMO energy level corresponds to an IP having a smaller absolutevalue (an IP that is less negative). Similarly, a higher LUMO energylevel corresponds to an electron affinity (EA) having a smaller absolutevalue (an EA that is less negative). On a conventional energy leveldiagram, with the vacuum level at the top, the LUMO energy level of amaterial is higher than the HOMO energy level of the same material. A“higher” HOMO or LUMO energy level appears closer to the top of such adiagram than a “lower” HOMO or LUMO energy level.

As used herein, and as would be generally understood by one skilled inthe art, a first work function is “greater than” or “higher than” asecond work function if the first work function has a higher absolutevalue. Because work functions are generally measured as negative numbersrelative to vacuum level, this means that a “higher” work function ismore negative. On a conventional energy level diagram, with the vacuumlevel at the top, a “higher” work function is illustrated as furtheraway from the vacuum level in the downward direction. Thus, thedefinitions of HOMO and LUMO energy levels follow a different conventionthan work functions.

More details on OLEDs, and the definitions described above, can be foundin U.S. Pat. No. 7,279,704, which is incorporated herein by reference inits entirety.

SUMMARY OF THE INVENTION

According to an embodiment, a compound is provided that includes aLigand L of Formula I

In the compound including the Ligand L of Formula I:

R¹ represents mono, or di-substitution, or no substitution;

R² represents mono, di, or tri-substitution, or no substitution;

X is selected from the group consisting of S, Se, SiRR′ and GeRR′;

R¹, R², R, and R′ are each independently selected from the groupconsisting of hydrogen, deuterium, halide, alkyl, cycloalkyl,heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl,cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl,carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl,sulfonyl, phosphino, and combinations thereof;

any adjacent substitutions or substituents of R¹, R², R, and R′ areoptionally linked together to form a ring;

the Ligand L is coordinated to a metal M having an atomic number of 40or greater, and

the Ligand L is optionally linked with other ligands to comprise atridentate, tetradentate, pentadentate or hexadentate ligand.

In some embodiments, the metal M is selected from the group consistingof Ir, Rh, Re, Ru, Os, Pt, Au, and Cu. In some embodiments, the metal Mis Ir.

According to another embodiment, a first device comprising a firstorganic light emitting device is also provided. The first organic lightemitting device can include an anode, a cathode, and an organic layer,disposed between the anode and the cathode. The organic layer caninclude a compound including a Ligand L of Formula I. The first devicecan be a consumer product, an organic light-emitting device, and/or alighting panel.

According to still another embodiment, a formulation the includes acompound having a Ligand L of Formula I is provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an organic light emitting device.

FIG. 2 shows an inverted organic light emitting device that does nothave a separate electron transport layer.

FIG. 3 shows the Ligand L of Formula I as disclosed herein.

DETAILED DESCRIPTION

Generally, an OLED comprises at least one organic layer disposed betweenand electrically connected to an anode and a cathode. When a current isapplied, the anode injects holes and the cathode injects electrons intothe organic layer(s). The injected holes and electrons each migratetoward the oppositely charged electrode. When an electron and holelocalize on the same molecule, an “exciton,” which is a localizedelectron-hole pair having an excited energy state, is formed. Light isemitted when the exciton relaxes via a photoemissive mechanism. In somecases, the exciton may be localized on an excimer or an exciplex.Non-radiative mechanisms, such as thermal relaxation, may also occur,but are generally considered undesirable.

The initial OLEDs used emissive molecules that emitted light from theirsinglet states (“fluorescence”) as disclosed, for example, in U.S. Pat.No. 4,769,292, which is incorporated by reference in its entirety.Fluorescent emission generally occurs in a time frame of less than 10nanoseconds.

More recently, OLEDs having emissive materials that emit light fromtriplet states (“phosphorescence”) have been demonstrated. Baldo et al.,“Highly Efficient Phosphorescent Emission from OrganicElectroluminescent Devices,” Nature, vol. 395, 151-154, 1998;(“Baldo-I”) and Baldo et al., “Very high-efficiency green organiclight-emitting devices based on electrophosphorescence,” Appl. Phys.Lett., vol. 75, No. 3, 4-6 (1999) (“Baldo-II”), which are incorporatedby reference in their entireties. Phosphorescence is described in moredetail in U.S. Pat. No. 7,279,704 at cols. 5-6, which are incorporatedby reference.

FIG. 1 shows an organic light emitting device 100. The figures are notnecessarily drawn to scale. Device 100 may include a substrate 110, ananode 115, a hole injection layer 120, a hole transport layer 125, anelectron blocking layer 130, an emissive layer 135, a hole blockinglayer 140, an electron transport layer 145, an electron injection layer150, a protective layer 155, a cathode 160, and a barrier layer 170.Cathode 160 is a compound cathode having a first conductive layer 162and a second conductive layer 164. Device 100 may be fabricated bydepositing the layers described, in order. The properties and functionsof these various layers, as well as example materials, are described inmore detail in U.S. Pat. No. 7,279,704 at cols. 6-10, which areincorporated by reference.

More examples for each of these layers are available. For example, aflexible and transparent substrate-anode combination is disclosed inU.S. Pat. No. 5,844,363, which is incorporated by reference in itsentirety. An example of a p-doped hole transport layer is m-MTDATA dopedwith F₄-TCNQ at a molar ratio of 50:1, as disclosed in U.S. PatentApplication Publication No. 2003/0230980, which is incorporated byreference in its entirety. Examples of emissive and host materials aredisclosed in U.S. Pat. No. 6,303,238 to Thompson et al., which isincorporated by reference in its entirety. An example of an n-dopedelectron transport layer is BPhen doped with Li at a molar ratio of 1:1,as disclosed in U.S. Patent Application Publication No. 2003/0230980,which is incorporated by reference in its entirety. U.S. Pat. Nos.5,703,436 and 5,707,745, which are incorporated by reference in theirentireties, disclose examples of cathodes including compound cathodeshaving a thin layer of metal such as Mg:Ag with an overlyingtransparent, electrically-conductive, sputter-deposited ITO layer. Thetheory and use of blocking layers is described in more detail in U.S.Pat. No. 6,097,147 and U.S. Patent Application Publication No.2003/0230980, which are incorporated by reference in their entireties.Examples of injection layers are provided in U.S. Patent ApplicationPublication No. 2004/0174116, which is incorporated by reference in itsentirety. A description of protective layers may be found in U.S. PatentApplication Publication No. 2004/0174116, which is incorporated byreference in its entirety.

FIG. 2 shows an inverted OLED 200. The device includes a substrate 210,a cathode 215, an emissive layer 220, a hole transport layer 225, and ananode 230. Device 200 may be fabricated by depositing the layersdescribed, in order. Because the most common OLED configuration has acathode disposed over the anode, and device 200 has cathode 215 disposedunder anode 230, device 200 may be referred to as an “inverted” OLED.Materials similar to those described with respect to device 100 may beused in the corresponding layers of device 200. FIG. 2 provides oneexample of how some layers may be omitted from the structure of device100.

The simple layered structure illustrated in FIGS. 1 and 2 is provided byway of non-limiting example, and it is understood that embodiments ofthe invention may be used in connection with a wide variety of otherstructures. The specific materials and structures described areexemplary in nature, and other materials and structures may be used.Functional OLEDs may be achieved by combining the various layersdescribed in different ways, or layers may be omitted entirely, based ondesign, performance, and cost factors. Other layers not specificallydescribed may also be included. Materials other than those specificallydescribed may be used. Although many of the examples provided hereindescribe various layers as comprising a single material, it isunderstood that combinations of materials, such as a mixture of host anddopant, or more generally a mixture, may be used. Also, the layers mayhave various sublayers. The names given to the various layers herein arenot intended to be strictly limiting. For example, in device 200, holetransport layer 225 transports holes and injects holes into emissivelayer 220, and may be described as a hole transport layer or a holeinjection layer. In one embodiment, an OLED may be described as havingan “organic layer” disposed between a cathode and an anode. This organiclayer may comprise a single layer, or may further comprise multiplelayers of different organic materials as described, for example, withrespect to FIGS. 1 and 2.

Structures and materials not specifically described may also be used,such as OLEDs comprised of polymeric materials (PLEDs) such as disclosedin U.S. Pat. No. 5,247,190 to Friend et al., which is incorporated byreference in its entirety. By way of further example, OLEDs having asingle organic layer may be used. OLEDs may be stacked, for example asdescribed in U.S. Pat. No. 5,707,745 to Forrest et al, which isincorporated by reference in its entirety. The OLED structure maydeviate from the simple layered structure illustrated in FIGS. 1 and 2.For example, the substrate may include an angled reflective surface toimprove out-coupling, such as a mesa structure as described in U.S. Pat.No. 6,091,195 to Forrest et al., and/or a pit structure as described inU.S. Pat. No. 5,834,893 to Bulovic et al., which are incorporated byreference in their entireties.

Unless otherwise specified, any of the layers of the various embodimentsmay be deposited by any suitable method. For the organic layers,preferred methods include thermal evaporation, ink-jet, such asdescribed in U.S. Pat. Nos. 6,013,982 and 6,087,196, which areincorporated by reference in their entireties, organic vapor phasedeposition (OVPD), such as described in U.S. Pat. No. 6,337,102 toForrest et al., which is incorporated by reference in its entirety, anddeposition by organic vapor jet printing (OVJP), such as described inU.S. Pat. No. 7,431,968, which is incorporated by reference in itsentirety. Other suitable deposition methods include spin coating andother solution based processes. Solution based processes are preferablycarried out in nitrogen or an inert atmosphere. For the other layers,preferred methods include thermal evaporation. Preferred patterningmethods include deposition through a mask, cold welding such asdescribed in U.S. Pat. Nos. 6,294,398 and 6,468,819, which areincorporated by reference in their entireties, and patterning associatedwith some of the deposition methods such as ink-jet and OVJD. Othermethods may also be used. The materials to be deposited may be modifiedto make them compatible with a particular deposition method. Forexample, substituents such as alkyl and aryl groups, branched orunbranched, and preferably containing at least 3 carbons, may be used insmall molecules to enhance their ability to undergo solution processing.Substituents having 20 carbons or more may be used, and 3-20 carbons isa preferred range. Materials with asymmetric structures may have bettersolution processibility than those having symmetric structures, becauseasymmetric materials may have a lower tendency to recrystallize.Dendrimer substituents may be used to enhance the ability of smallmolecules to undergo solution processing.

Devices fabricated in accordance with embodiments of the presentinvention may further optionally comprise a barrier layer. One purposeof the barrier layer is to protect the electrodes and organic layersfrom damaging exposure to harmful species in the environment includingmoisture, vapor and/or gases, etc. The barrier layer may be depositedover, under or next to a substrate, an electrode, or over any otherparts of a device including an edge. The barrier layer may comprise asingle layer, or multiple layers. The barrier layer may be formed byvarious known chemical vapor deposition techniques and may includecompositions having a single phase as well as compositions havingmultiple phases. Any suitable material or combination of materials maybe used for the barrier layer. The barrier layer may incorporate aninorganic or an organic compound or both. The preferred barrier layercomprises a mixture of a polymeric material and a non-polymeric materialas described in U.S. Pat. No. 7,968,146, PCT Pat. Application Nos.PCT/US2007/023098 and PCT/US2009/042829, which are herein incorporatedby reference in their entireties. To be considered a “mixture”, theaforesaid polymeric and non-polymeric materials comprising the barrierlayer should be deposited under the same reaction conditions and/or atthe same time. The weight ratio of polymeric to non-polymeric materialmay be in the range of 95:5 to 5:95. The polymeric material and thenon-polymeric material may be created from the same precursor material.In one example, the mixture of a polymeric material and a non-polymericmaterial consists essentially of polymeric silicon and inorganicsilicon.

Devices fabricated in accordance with embodiments of the invention maybe incorporated into a wide variety of consumer products, including flatpanel displays, computer monitors, medical monitors, televisions,billboards, lights for interior or exterior illumination and/orsignaling, heads up displays, fully transparent displays, flexibledisplays, laser printers, telephones, cell phones, personal digitalassistants (PDAs), laptop computers, digital cameras, camcorders,viewfinders, micro-displays, 3-D displays, vehicles, a large area wall,theater or stadium screen, or a sign. Various control mechanisms may beused to control devices fabricated in accordance with the presentinvention, including passive matrix and active matrix. Many of thedevices are intended for use in a temperature range comfortable tohumans, such as 18 degrees C. to 30 degrees C., and more preferably atroom temperature (20-25 degrees C), but could be used outside thistemperature range, for example, from −40 degree C to +80 degree C.

The materials and structures described herein may have applications indevices other than OLEDs. For example, other optoelectronic devices suchas organic solar cells and organic photodetectors may employ thematerials and structures. More generally, organic devices, such asorganic transistors, may employ the materials and structures.

The term “halo” or “halogen” as used herein includes fluorine, chlorine,bromine, and iodine.

The term “alkyl” as used herein contemplates both straight and branchedchain alkyl radicals. Preferred alkyl groups are those containing fromone to fifteen carbon atoms and includes methyl, ethyl, propyl,isopropyl, butyl, isobutyl, tert-butyl, and the like. Additionally, thealkyl group may be optionally substituted.

The term “cycloalkyl” as used herein contemplates cyclic alkyl radicals.Preferred cycloalkyl groups are those containing 3 to 7 carbon atoms andincludes cyclopropyl, cyclopentyl, cyclohexyl, and the like.Additionally, the cycloalkyl group may be optionally substituted.

The term “alkenyl” as used herein contemplates both straight andbranched chain alkene radicals. Preferred alkenyl groups are thosecontaining two to fifteen carbon atoms. Additionally, the alkenyl groupmay be optionally substituted.

The term “alkynyl” as used herein contemplates both straight andbranched chain alkyne radicals. Preferred alkyl groups are thosecontaining two to fifteen carbon atoms. Additionally, the alkynyl groupmay be optionally substituted.

The terms “aralkyl” or “arylalkyl” as used herein are usedinterchangeably and contemplate an alkyl group that has as a substituentan aromatic group. Additionally, the aralkyl group may be optionallysubstituted.

The term “heterocyclic group” as used herein contemplates non-aromaticcyclic radicals. Preferred heterocyclic groups are those containing 3 or7 ring atoms which includes at least one hetero atom, and includescyclic amines such as morpholino, piperdino, pyrrolidino, and the like,and cyclic ethers, such as tetrahydrofuran, tetrahydropyran, and thelike. Additionally, the heterocyclic group may be optionallysubstituted.

The term “aryl” or “aromatic group” as used herein contemplatessingle-ring groups and polycyclic ring systems. The polycyclic rings mayhave two or more rings in which two carbons are common to two adjoiningrings (the rings are “fused”) wherein at least one of the rings isaromatic, e.g., the other rings can be cycloalkyls, cycloalkenyls, aryl,heterocycles, and/or heteroaryls. Additionally, the aryl group may beoptionally substituted.

The term “heteroaryl” as used herein contemplates single-ringhetero-aromatic groups that may include from one to three heteroatoms,for example, pyrrole, furan, thiophene, imidazole, oxazole, thiazole,triazole, pyrazole, pyridine, pyrazine and pyrimidine, and the like. Theterm heteroaryl also includes polycyclic hetero-aromatic systems havingtwo or more rings in which two atoms are common to two adjoining rings(the rings are “fused”) wherein at least one of the rings is aheteroaryl, e.g., the other rings can be cycloalkyls, cycloalkenyls,aryl, heterocycles, and/or heteroaryls. Additionally, the heteroarylgroup may be optionally substituted.

The alkyl, cycloalkyl, alkenyl, alkynyl, aralkyl, heterocyclic group,aryl, and heteroaryl may be optionally substituted with one or moresubstituents selected from the group consisting of hydrogen, deuterium,halogen, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy,amino, cyclic amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl,alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acid, ether,ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, andcombinations thereof.

As used herein, “substituted” indicates that a substituent other than His bonded to the relevant position, such as carbon. Thus, for example,where R¹ is mono-substituted, then one R¹ must be other than H.Similarly, where R¹ is di-substituted, then two of R¹ must be other thanH. Similarly, where R¹ is unsubstituted, R¹ is hydrogen for allavailable positions.

The “aza” designation in the fragments described herein, i.e.aza-dibenzofuran, aza-dibenzonethiophene, etc. means that one or more ofthe C—H groups in the respective fragment can be replaced by a nitrogenatom, for example, and without any limitation, azatriphenyleneencompasses both dibenzo[f,h]quinoxaline and dibenzo[f,h]quinoline. Oneof ordinary skill in the art can readily envision other nitrogen analogsof the aza-derivatives described above, and all such analogs areintended to be encompassed by the terms as set forth herein.

It is to be understood that when a molecular fragment is described asbeing a substituent or otherwise attached to another moiety, its namemay be written as if it were a fragment (e.g. naphthyl, dibenzofuryl) oras if it were the whole molecule (e.g. naphthalene, dibenzofuran). Asused herein, these different ways of designating a substituent orattached fragment are considered to be equivalent.

Iridium tris pyridyl-pyridine complexes offer a platform for blueemission that does not require the use of electron withdrawingsubstituents. Intrinsically, the unfunctionalized compounds emit from ahigh energy triplet state with a peak maximum around 450 nm. However, atroom temperature, the emission spectra is broadened significantlyresulting in a decrease in the practical blue emission color. It hasbeen shown that removing a sterically bulky ligation-directingsubstituent results in a substantial improvement of the practicalemission color at room temperature. While not wishing to be bound bytheory, it is believed that this effect is due to less distortion in theexcited state. This disclosure describes a further improvement ofpyridyl-pyridine complexes which provides ligation selectivity andrigidification of the ligand by tethering the pyridyl-pyridine ligandstogether with a single atom, such as silicon or sulfur, in order toenhance the emission color to give more blue emission at roomtemperature.

According to one embodiment, a compound including a Ligand L of FormulaI:

Formula I is disclosed.In the compound including the Ligand L of Formula I:

R¹ represents mono, or di-substitution, or no substitution;

R² represents mono, di, or tri-substitution, or no substitution;

X is selected from the group consisting of S, Se, SiRR′ and GeRR′;

R¹, R², R, and R′ are each independently selected from the groupconsisting of hydrogen, deuterium, halide, alkyl, cycloalkyl,heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl,cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl,carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl,sulfonyl, phosphino, and combinations thereof;

any adjacent substitutions or substituents of R¹, R², R, and R′ areoptionally linked together to form a ring;

the Ligand L is coordinated to a metal M having an atomic number of 40or greater; and

the Ligand L is optionally linked with other ligands to comprise atridentate, tetradentate, pentadentate or hexadentate ligand.

In some embodiments, the metal M is selected from the group consistingof Ir, Rh, Re, Ru, Os, Pt, Au, and Cu. In some embodiments, the metal Mis Ir.

In some embodiments, the compound is homoleptic having formula of IrL₃.In some embodiments, the compound is a facial isomer, while the compoundis a meridional isomer in other embodiments. In still other embodiments,the compound is heteroleptic.

In some embodiments, R¹ and R² are each independently selected from thegroup consisting of hydrogen, deuterium, alkyl, cycloalkyl, aryl,heteroaryl, and combinations thereof. In some embodiments, at least oneof R¹ and R² comprises a moiety selected from the group consisting ofphenyl, toluene, biphenyl and tetraphenyl. In some embodiments, both R¹and R² comprises a moiety selected from the group consisting of phenyl,toluene, biphenyl and tetraphenyl. In some embodiments, R¹ ismono-substitution on the ortho position to N.

In some embodiments, R and R′ are each independently selected from thegroup consisting of alkyl, aryl, heteroaryl, and combinations thereof.

In some more specific embodiments, the compound is selected from thegroup consisting of:

According to another aspect of the present disclosure, a first device isalso provided. The first device includes a first organic light emittingdevice, that includes an anode, a cathode, and an organic layer disposedbetween the anode and the cathode. The organic layer can include a hostand a phosphorescent dopant. The organic layer can include a compoundcomprising a Ligand L of Formula I and any variations of the compound asdescribed herein.

The first device can be one or more of a consumer product, an organiclight-emitting device and a lighting panel. The organic layer can be anemissive layer and the compound can be an emissive dopant in someembodiments, while the compound can be a non-emissive dopant in otherembodiments.

The organic layer can also include a host. In some embodiments, the hostcan include a metal complex. The host can be a triphenylene containingbenzo-fused thiophene or benzo-fused furan. Any substituent in the hostcan be an unfused substituent independently selected from the groupconsisting of C_(n)H_(2n+1), OC_(n)H_(2n+1), OAr₁, N(C_(n)H_(2n+1))₂,N(Ar₁)(Ar₂), CH═CH—C_(n)H_(2n+1), C═C≡C_(n)H_(2n+1), Ar₁, Ar₁—Ar₂,C_(n)H_(2n)—Ar₁, or no substitution. In the preceding substituents n canrange from 1 to 10; and Ar₁ and Ar₂ can be independently selected fromthe group consisting of benzene, biphenyl, naphthalene, triphenylene,carbazole, and heteroaromatic analogs thereof.

The host can be a compound selected from the group consisting ofcarbazole, dibenzothiphene, dibenzofuran, dibenzoselenophene,azacarbazole, aza-dibenzothiophene, aza-dibenzofuran, andaza-dibenzoselenophene. The host can include a metal complex. The hostcan be a specific compound selected from the group consisting of:

and combinations thereof.

In yet another aspect of the present disclosure, a formulation thatcomprises a compound comprising a Ligand L of Formula I and anyvariations of the compound as described herein. The formulation caninclude one or more components selected from the group consisting of asolvent, a host, a hole injection material, hole transport material, andan electron transport layer material, disclosed herein.

Combination with Other Materials

The materials described herein as useful for a particular layer in anorganic light emitting device may be used in combination with a widevariety of other materials present in the device. For example, emissivedopants disclosed herein may be used in conjunction with a wide varietyof hosts, transport layers, blocking layers, injection layers,electrodes and other layers that may be present. The materials describedor referred to below are non-limiting examples of materials that may beuseful in combination with the compounds disclosed herein, and one ofskill in the art can readily consult the literature to identify othermaterials that may be useful in combination.

HIL/HTL:

A hole injecting/transporting material to be used in the presentinvention is not particularly limited, and any compound may be used aslong as the compound is typically used as a hole injecting/transportingmaterial. Examples of the material include, but not limit to: aphthalocyanine or porphyrin derivative; an aromatic amine derivative; anindolocarbazole derivative; a polymer containing fluorohydrocarbon; apolymer with conductivity dopants; a conducting polymer, such asPEDOT/PSS; a self-assembly monomer derived from compounds such asphosphonic acid and silane derivatives; a metal oxide derivative, suchas MoO_(x); a p-type semiconducting organic compound, such as1,4,5,8,9,12-Hexaazatriphenylenehexacarbonitrile; a metal complex, and across-linkable compounds.

Examples of aromatic amine derivatives used in HIL or HTL include, butnot limit to the following general structures:

Each of Ar¹ to Ar⁹ is selected from the group consisting aromatichydrocarbon cyclic compounds such as benzene, biphenyl, triphenyl,triphenylene, naphthalene, anthracene, phenalene, phenanthrene,fluorene, pyrene, chrysene, perylene, azulene; group consisting aromaticheterocyclic compounds such as dibenzothiophene, dibenzofuran,dibenzoselenophene, furan, thiophene, benzofuran, benzothiophene,benzoselenophene, carbazole, indolocarbazole, pyridylindole,pyrrolodipyridine, pyrazole, imidazole, triazole, oxazole, thiazole,oxadiazole, oxatriazole, dioxazole, thiadiazole, pyridine, pyridazine,pyrimidine, pyrazine, triazine, oxazine, oxathiazine, oxadiazine,indole, benzimidazole, indazole, indoxazine, benzoxazole, benzisoxazole,benzothiazole, quinoline, isoquinoline, cinnoline, quinazoline,quinoxaline, naphthyridine, phthalazine, pteridine, xanthene, acridine,phenazine, phenothiazine, phenoxazine, benzofuropyridine,furodipyridine, benzothienopyridine, thienodipyridine,benzoselenophenopyridine, and selenophenodipyridine; and groupconsisting 2 to 10 cyclic structural units which are groups of the sametype or different types selected from the aromatic hydrocarbon cyclicgroup and the aromatic heterocyclic group and are bonded to each otherdirectly or via at least one of oxygen atom, nitrogen atom, sulfur atom,silicon atom, phosphorus atom, boron atom, chain structural unit and thealiphatic cyclic group. Wherein each Ar is further substituted by asubstituent selected from the group consisting of hydrogen, deuterium,halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy,amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl,heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile,isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinationsthereof.

In one aspect, Ar¹ to Ar⁹ is independently selected from the groupconsisting of:

wherein k is an integer from 1 to 20; X¹⁰¹ to X¹⁰⁸ is C (including CH)or N; Z¹⁰¹ is NAr¹, O, or S; Ar¹ has the same group defined above.

Examples of metal complexes used in HIL or HTL include, but not limit tothe following general formula:

wherein Met is a metal, which can have an atomic weight greater than 40;(Y¹⁰¹-Y¹⁰²) is a bidentate ligand, Y¹⁰¹ and Y¹⁰² are independentlyselected from C, N, O, P, and S; L¹⁰¹ is an ancillary ligand; k′ is aninteger value from 1 to the maximum number of ligands that may beattached to the metal; and k′+k″ is the maximum number of ligands thatmay be attached to the metal.

In one aspect, (Y¹⁰¹-Y¹⁰²) is a 2-phenylpyridine derivative. In anotheraspect, (Y¹⁰¹-Y¹⁰²) is a carbene ligand. In another aspect, Met isselected from Ir, Pt, Os, and Zn. In a further aspect, the metal complexhas a smallest oxidation potential in solution vs. Fc⁺/Fc couple lessthan about 0.6 V.

Host:

The light emitting layer of the organic EL device of the presentinvention preferably contains at least a metal complex as light emittingmaterial, and may contain a host material using the metal complex as adopant material. Examples of the host material are not particularlylimited, and any metal complexes or organic compounds may be used aslong as the triplet energy of the host is larger than that of thedopant. While the Table below categorizes host materials as preferredfor devices that emit various colors, any host material may be used withany dopant so long as the triplet criteria is satisfied.

Examples of metal complexes used as host are preferred to have thefollowing general formula:

wherein Met is a metal; (Y¹⁰³-Y¹⁰⁴) is a bidentate ligand, Y¹⁰³ and Y¹⁰⁴are independently selected from C, N, O, P, and S; L¹⁰¹ is an anotherligand; k′ is an integer value from 1 to the maximum number of ligandsthat may be attached to the metal; and k′+k″ is the maximum number ofligands that may be attached to the metal.

In one aspect, the metal complexes are:

wherein (O—N) is a bidentate ligand, having metal coordinated to atoms Oand N.

In another aspect, Met is selected from Ir and Pt. In a further aspect,(Y¹⁰³-Y¹⁰⁴) is a carbene ligand.

Examples of organic compounds used as host are selected from the groupconsisting aromatic hydrocarbon cyclic compounds such as benzene,biphenyl, triphenyl, triphenylene, naphthalene, anthracene, phenalene,phenanthrene, fluorene, pyrene, chrysene, perylene, azulene; groupconsisting aromatic heterocyclic compounds such as dibenzothiophene,dibenzofuran, dibenzoselenophene, furan, thiophene, benzofuran,benzothiophene, benzoselenophene, carbazole, indolocarbazole,pyridylindole, pyrrolodipyridine, pyrazole, imidazole, triazole,oxazole, thiazole, oxadiazole, oxatriazole, dioxazole, thiadiazole,pyridine, pyridazine, pyrimidine, pyrazine, triazine, oxazine,oxathiazine, oxadiazine, indole, benzimidazole, indazole, indoxazine,benzoxazole, benzisoxazole, benzothiazole, quinoline, isoquinoline,cinnoline, quinazoline, quinoxaline, naphthyridine, phthalazine,pteridine, xanthene, acridine, phenazine, phenothiazine, phenoxazine,benzofuropyridine, furodipyridine, benzothienopyridine,thienodipyridine, benzoselenophenopyridine, and selenophenodipyridine;and group consisting 2 to 10 cyclic structural units which are groups ofthe same type or different types selected from the aromatic hydrocarboncyclic group and the aromatic heterocyclic group and are bonded to eachother directly or via at least one of oxygen atom, nitrogen atom, sulfuratom, silicon atom, phosphorus atom, boron atom, chain structural unitand the aliphatic cyclic group. Wherein each group is furthersubstituted by a substituent selected from the group consisting ofhydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl,alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl,alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester,nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, andcombinations thereof.

In one aspect, host compound contains at least one of the followinggroups in the molecule:

wherein R¹⁰¹ to R¹⁰⁷ is independently selected from the group consistingof hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl,arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl,heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylicacids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl,phosphino, and combinations thereof, when it is aryl or heteroaryl, ithas the similar definition as Ar's mentioned above. k is an integer from0 to 20 or 1 to 20; k′″ is an integer from 0 to 20. X¹⁰¹ to X¹⁰⁸ isselected from C (including CH) or N. Z¹⁰¹ and Z¹⁰² is selected fromNR¹⁰¹, O, or S.

HBL:

A hole blocking layer (HBL) may be used to reduce the number of holesand/or excitons that leave the emissive layer. The presence of such ablocking layer in a device may result in substantially higherefficiencies as compared to a similar device lacking a blocking layer.Also, a blocking layer may be used to confine emission to a desiredregion of an OLED.

In one aspect, compound used in HBL contains the same molecule or thesame functional groups used as host described above.

In another aspect, compound used in HBL contains at least one of thefollowing groups in the molecule:

wherein k is an integer from 1 to 20; L¹⁰¹ is an another ligand, k′ isan integer from 1 to 3.

ETL:

Electron transport layer (ETL) may include a material capable oftransporting electrons. Electron transport layer may be intrinsic(undoped), or doped. Doping may be used to enhance conductivity.Examples of the ETL material are not particularly limited, and any metalcomplexes or organic compounds may be used as long as they are typicallyused to transport electrons.

In one aspect, compound used in ETL contains at least one of thefollowing groups in the molecule:

wherein R¹⁰¹ is selected from the group consisting of hydrogen,deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy,aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl,aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile,isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinationsthereof, when it is aryl or heteroaryl, it has the similar definition asAr's mentioned above. Ar¹ to Ar³ has the similar definition as Ar'smentioned above. k is an integer from 1 to 20. X¹⁰¹ to X¹⁰⁸ is selectedfrom C (including CH) or N.

In another aspect, the metal complexes used in ETL contains, but notlimit to the following general formula:

wherein (O—N) or (N—N) is a bidentate ligand, having metal coordinatedto atoms O, N or N, N; L¹⁰¹ is another ligand; k′ is an integer valuefrom 1 to the maximum number of ligands that may be attached to themetal.

In any above-mentioned compounds used in each layer of the OLED device,the hydrogen atoms can be partially or fully deuterated. Thus, anyspecifically listed substituent, such as, without limitation, methyl,phenyl, pyridyl, etc. encompasses undeuterated, partially deuterated,and fully deuterated versions thereof. Similarly, classes ofsubstituents such as, without limitation, alkyl, aryl, cycloalkyl,heteroaryl, etc. also encompass undeuterated, partially deuterated, andfully deuterated versions thereof.

In addition to and/or in combination with the materials disclosedherein, many hole injection materials, hole transporting materials, hostmaterials, dopant materials, exiton/hole blocking layer materials,electron transporting and electron injecting materials may be used in anOLED. Non-limiting examples of the materials that may be used in an OLEDin combination with materials disclosed herein are listed in Table 1,below. Table 1 lists non-limiting classes of materials, non-limitingexamples of compounds for each class, and references that disclose thematerials.

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EXPERIMENTAL

Facial-tris Iridium pyridyl-pyridine complexes offer a unique platformthat enables blue emitting phosphorescent complexes without the use ofelectronic substituents attached to the aromatic rings. It is discoveredthat the position of the nitrogen is an important factor determining thecolor of the compound as with the unsubstituted parent ligand there aretwo possible ligation sites. Hence site blocking/directing substituents,often fluoro or alkyl, can be used to direct ligation to the desiredisomer. While the use of site directing substituents is desirable from asynthetic yield and isolation standpoint, it can compromise otherproperties of the complex. For example, fluorine often blue-shifts theemission energy; however, blue phosphorescent complexes that havefluorine substituted in analogous positions for a phenylpyridine ligand,such as the well-studied FIrpic complex (iridium (III)bis(4,6-difluorophenylpyridinato) picolinate), have been shown to beunstable in electroluminescent devices. Furthermore, bulky alkylsubstituents, such as methyl groups, can have steric influences on theplane of the bidentate ligand, resulting in a significant red-shiftingeffect at room temperature. This effect is observed when comparingmethyl blocked pyridyl-pyridine emitters to analogous non-blockedcomplexes.

The invention described here is a modification to the pyridyl-pyridineligand that provides both a site direction for synthesis of the desiredtris isomer in high yield as well as a rigidifying effect on the ligandin order to provide more a saturated blue emission at room temperature.Both of these effects can be accomplished by bridging the pyridylpyridine ligand with a single non-conjugating atom linker, such assilicon or sulfur. Silicon or sulfur, or larger atoms, may be preferredover oxygen due to the effect of the atom's size on the ligand biteangle for complexation.

Density functional theory was used to minimize the ground state geometryof the complexes. Calculations were performed using theB3LYP/cep-31g/THF functional, basis set and solvent polarization,respectively. The relavent bond angles and bond lengths for the C—C—C,Ir—N and Ir—C bonds are defined in bold:

TABLE 2 Bond angles and bond lengths for invention compounds andcomparative examples. Bond Ir-N Ir-C Structure angle (°) (Å) (Å)Comparative Example 1

116.3 2.17 2.03 Comparative Example 2

125.6 2.41 2.03 Compound 1

121.4 2.25 2.04 Compound 2

119.3 2.21 2.04

Table 2 shows the preferred structures where the bridging atom is largeenough to bridge the two pyridine rings without significant distortionaround the metal. The data shows that where the bridging atom is oxygen,the bond angle (125.6°) and Ir—N bond length (2.41 Å) are significantlydistorted compared to Comparative Example 1 and the invention compounds.For a non-strained ring system, the bond angle should be close to anideal 120° as is the case for Compound 1 and 2.

Table 3 shows the energy level calculations for bridged and unbridgedpyridyl-pyridine ligands.

TABLE 3 Energy level calculations HOMO LUMO Gap Dipole S1_(gas) T1_(gas)Structure (eV) (eV) (eV) (Debye) (nm) (nm) Comparative Example 1

−5.87 −1.89 −3.91 16.22 395 462 Compound 1

−6.11 −2.07 −4.04 14.44 390 445 Compound 2

−5.71 −1.74 −3.97 14.74 386 463 Compound 3

−5.79 −1.83 −3.96 14.29 386 465

Synthetic Examples Synthesis of Ligand 1 Synthesis of2′-chloro-3-fluoro-2,3′-bipyridine

A solution of isopropylmagnesium chloride in THF (2.0 M, 20.05 ml, 40.1mmol) was dissolved in THF (25 ml) and cooled in ice/water bath, before2-bromo-3-fluoropyridine (3.72 ml, 36.8 mmol) was slowly added viasyringe. The resulting solution in stirred at room temperature for 1hour, then a zinc(II) chloride solution in THF (0.5 M, 80 ml, 40.1 mmol)was added via syringe and stirred at room temperature overnight, forminga nearly colorless, heterogeneous mixture. Separately, a flaskcontaining 2-chloro-3-iodopyridine (8 g, 33.4 mmol) and Pd(PPh₃)₄ (1.930g, 1.671 mmol) was degassed, then THF (100 ml) was added and theresulting solution was warmed to near reflux. The zinc chloridesuspension was added via cannula to the 2-chloro-3iodopyridine solutionand the resulting yellow mixture was stirred at reflux over the weekend,cooled to room temperature, and then filtered through celite. Solventremoval from the filtrates was followed by partitioning between EtOAcand basic water. The aqueous layer was extracted with EtOAc three times,the combined organics were washed with brine, dried, and the solvent asremoved. After coating on celite, the product was eluted on a 200 gsilica column using 10-25% EtOAc in DCM, collecting pale yellowR_(f)˜0.45 fractions, yielding a pale yellow solid, 5.29 g (76%).

Synthesis of ethyl 3-((3-fluoro-[2,3′-bipyridin]-2′-yl)thio)propanoate

2′-chloro-3-fluoro-2,3′-bipyridine (4.96 g. 23.78 mmol), Pd₂(dba)₃(0.544 g, 0.594 mmol), (oxybis(2,1-phenylene))bis(diphenylphosphine)(0.640 g, 1.189 mmol), and potassium carbonate (8.21 g, 59.4 mmol) werecombined in a 3-neck flask, vacuum/backfilled three times with nitrogen,and degassed. Toluene (120 ml) was added and heated to a gentle reflux,which produced a light orange mixture. Ethyl 3-mercaptopropanoate (3.31ml, 26.2 mmol) was added and the reaction mixture was heated at refluxovernight. The reaction mixture was cooled to room temperature, dilutedwith EtOAc and filtered through celite. After solvent removal from thefiltrate, the residue was coated on celite and eluted on a 120 g silicacolumn using 25% EtOAc/DCM, then 50% EtOAc/DCM. The resulting very paleyellow fractions with R_(f)˜0.6 (50% EtOAc/DCM) was collected yielding ayellow-stained oil containing ethyl3-((3-fluoro-[2,3′-bipyridin]-2′-yl)thio)propanoate, 6.95 g (95%).

Synthesis of thieno[2,3-b:4,5-b′]dipyridine

A solution of ethyl 3-((3-fluoro-[2,3′-bipyridin]-2′-yl)thio)propanoate(6.20 g, 20.24 mmol) in dioxane (120 ml) was added via cannula to anitrogen-purged flask containing potassium tert-butoxide (3.41 g. 30.4mmol) and the mixture was heated at reflux overnight with efficientstirring. The mixture first became a sludge, then a more fluidsuspension. The reaction mixture was cooled to room temperature,partitioned between EtOAc and water/brine, separated, and the aqueouslayer was extracted three more times with EtOAc. The combined organicswere washed with brine, dried, and the solvent was removed. The residuewas coated on celite and eluted on a 120 g silica column using 1:1EtOAc/DCM, collecting R_(f)˜0.35 fractions, yielding 3.44 g of yellowishsolid that was distilled on a kugelrohr (170-205° C.) to yield a nearlycolorless oil containing thieno[2,3-b:4,5-b′]dipyridine thatcrystallizes at room temperature, 3.37 g (89%).

It is understood that the various embodiments described herein are byway of example only, and are not intended to limit the scope of theinvention. For example, many of the materials and structures describedherein may be substituted with other materials and structures withoutdeviating from the spirit of the invention. The present invention asclaimed may therefore include variations from the particular examplesand preferred embodiments described herein, as will be apparent to oneof skill in the art. It is understood that various theories as to whythe invention works are not intended to be limiting.

We claim:
 1. A compound comprising a Ligand L of Formula 1:

wherein R¹ represents mono, or di-substitution, or no substitution;wherein R² represents mono, di, or tri-substitution, or no substitution;wherein X is selected from the group consisting of S, Se, SiRR′ andGeRR′; wherein R¹, R², R, and R′ are each independently selected fromthe group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl,heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl,cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl,carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl,sulfonyl, phosphino, and combinations thereof; wherein any adjacentsubstitutions are optionally linked together to form a ring; wherein theLigand L is coordinated to a metal M having an atomic number of 40 orgreater; and wherein the Ligand L is optionally linked with otherligands to comprise a tridentate, tetradentate, pentadentate orhexadentate ligand.
 2. The compound of claim 1, wherein M is selectedfrom the group consisting of Ir, Rh, Re, Ru, Os, Pt, Au, and Cu.
 3. Thecompound of claim 1, wherein M is Ir.
 4. The compound of claim 1,wherein the compound is homoleptic having formula of IrL₃.
 5. Thecompound of claim 4, wherein said compound is a facial isomer.
 6. Thecompound of claim 4, wherein said compound is a meridional isomer. 7.The compound of claim 1, wherein the compound is heteroleptic.
 8. Thecompound of claim 1, wherein R¹, and R² are each independently selectedfrom the group consisting of hydrogen, deuterium, alkyl, cycloalkyl,aryl, heteroaryl, and combinations thereof.
 9. The compound of claim 1,wherein at least one of R¹ and R² comprises a moiety selected from thegroup consisting of phenyl, toluene, biphenyl and tetraphenyl.
 10. Thecompound of claim 1, wherein R, and R′ are each independently selectedfrom the group consisting of alkyl, aryl, heteroaryl, and combinationsthereof.
 11. The compound of claim 1, wherein R¹ is mono-substitution onthe ortho position to N.
 12. The compound of claim 1, wherein thecompound is selected from the group consisting of:


13. A first device comprising a first organic light emitting device, thefirst organic light emitting device comprising: an anode; a cathode; andan organic layer, disposed between the anode and the cathode, comprisinga compound comprising a Ligand L of Formula I:

wherein R¹ represents mono, or di-substitution, or no substitution;wherein R² represents mono, di, or tri-substitution, or no substitution;wherein X is selected from the group consisting of S, Se, SiRR′ andGeRR′; wherein R¹, R², R, and R′ are each independently selected fromthe group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl,heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl,cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl,carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl,sulfonyl, phosphino, and combinations thereof; wherein any adjacentsubstitutions are optionally linked together to form a ring; wherein theLigand L is coordinated to a metal M having an atomic number of 40 orgreater; and wherein the Ligand L is optionally linked with otherligands to comprise a tridentate, tetradentate, pentadentate orhexadentate ligand.
 14. The first device of claim 13, wherein theorganic layer is an emissive layer and the compound is an emissivedopant.
 15. The first device of claim 13, wherein the organic layer isan emissive layer and the compound is a non-emissive dopant.
 16. Thefirst device of claim 13, wherein the organic layer further comprises ahost material.
 17. The first device of claim 16, wherein the hostmaterial comprises a triphenylene containing benzo-fused thiophene orbenzo-fused furan; wherein any substituent in the host material is anunfused substituent independently selected from the group consisting ofC_(n)H_(2n+1), OC_(n)H_(2n+1), OAr₁, N(C_(n)H_(2n+1))₂, N(Ar₁)(Ar₂),CH═CH—C_(n)H_(2n+1), C≡C—C_(n)H_(2n+1), Ar₁, Ar₁—Ar₂, C_(n)H_(2n)—Ar₁,or no substitution; wherein n is from 1 to 10; and wherein Ar₁ and Ar₂are independently selected from the group consisting of benzene,biphenyl, naphthalene, triphenylene, carbazole, and heteroaromaticanalogs thereof.
 18. The first device of claim 16, wherein the hostmaterial comprises at least one chemical group selected from the groupconsisting of carbazole, dibenzothiphene, dibenzofuran,dibenzoselenophene, azacarbazole, aza-dibenzothiophene,aza-dibenzofuran, and aza-dibenzoselenophene.
 19. The first device ofclaim 16, wherein the host material is selected from the groupconsisting of:

and combinations thereof.
 20. A formulation comprising a compoundcomprising a Ligand L of Formula I:

wherein R¹ represents mono, or di-substitution, or no substitution;wherein R² represents mono, di, or tri-substitution, or no substitution;wherein X is selected from the group consisting of S, Se, SiRR′ andGeRR′; wherein R¹, R², R, and R′ are each independently selected fromthe group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl,heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl,cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl,carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl,sulfonyl, phosphino, and combinations thereof; wherein any adjacentsubstitutions are optionally linked together to form a ring; wherein theLigand L is coordinated to a metal M having an atomic number of 40 orgreater; and wherein the Ligand L is optionally linked with otherligands to comprise a tridentate, tetradentate, pentadentate orhexadentate ligand.